AC clutch doesn't engage
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  1. #1
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    AC clutch doesn't engage

    My A/C clutch is not engaging. The fan does turn on. AC does not work. I tried a quick charge but the clutch still hasn't engaged so I was hoping to start by being able to test out relay 384. (99' passat 1.8 turbo).

    I saw the following post (at the bottom) by kenblasko. This may be a stupid question, but is this the easiest way to test the relay? Is there a way to test it with a multimeter with the relay out of the car? If not, can anyone please provide slightly better instructions to a newb to test, or perhaps an easier test? And an even dumber question, will a 12 volt battery work on the test below?
    Thanks


    "384 is not a simple relay but a control module (probably solid state relay) that controls the A/C clutch. Pull module 384 and jumper 12 volts to the plug connector corresponding to pin 8 of 384. That puts 12 volts directly to the A/C clutch. Positive should be on connector to pin 2. If the clutch engages, then either control module 384 is bad or possibly the A/C switch on dash, the ambient temperature switch, the A/C pressure switch or blower fan switch all wired in series and connected to pin 9 of 384. If you turn A/C switch on you should get positive on connector to pin 9. Pin 3 is ground. Pin 1 goes to the ECM and pin 4 goes to the instrument panel control module."

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  3. #2
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    It could be that there is no gass in the system. There is a trinary switch located in one of the pipes,it senses wether the presure is too high or too low and then kicks out the compressor

  4. #3
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    Still not working - more info

    I did some investigation and also brought the car into the shop. The shop couldn't figure out what it was (though I did get charged ) but did do some analysis and recommended I go to the VW dealer. Here if the new info.

    About 2 months ago, water got under the car due to drains under battery. It's still some what moist unfortunately.

    1. I switched the A/C from my friends similar Passat, and it still didn't work. So looks like Relay is ok
    2. Tech checked all the pressure. He said the a/c system itself is fine. He was able to get the A/C going by applying 12 volts to the ac clutch. He said the compressor/clutch etc. worked great and the car cooled down. He said he tested as many things as he knew how to but thinks it's electrical, and possibily the a/c control module but he didn't really know.
    3. I flipped over the carpet (though I didn't open the black box) of the CCM due to other searches I found on here on water getting in (water came in due to clogged drains a couple months ago, though I'm not sure this is what's causing this). The wires were still moist. I dried as much as I could, and have it pulled up to see if it dries more tonight. I couldn't actually pull the carpet enough to open the black box though, I'll pull harder in the next couple days...

    Should I wait until everything I dry before thinking the CCM or wireharness is bad? Could everything work once it's completely dry? Is there a way to know which CCM wire is for the A/C - I'll try and check them all over this weekend. Unfortunately I don't know the best way to get the carpets to dry fast (looks like they can absorb lots of water).

    Lots of questions, but I'm not sure what to do since everything but the A/C appears to work just fine. Lights, blinkers, alarm, drunk, etc., no problems yet.

    Is it premature to think the CCM or wires are at fault here?

  5. #4
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    Does your blower work? Does your a/c indicator light come on when you turn the a/c on? There's an ambient temperature switch and also the a/c pressure switch that could be bad. Did the shop test these switches? So you swapped relay 384 and yours worked in the other car? If 384 is good and a/c clutch engaged, then its either the temp switch, pressure switch, blower switch, a/c switch, fuse, or wiring problem. I don't believe the CCM or CCM wires could cause the a/c not to work.

  6. #5
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    Hi Ken,

    Blower works and a/c indicator light comes on. Unfortunately when I swapped 384 I didn't try mine in his, only his in mine (I realized this mistake after). But his should have worked unless I have perhaps multiple things wrong.

    Where are the pressure switch and temp switch located - can I test those easily?

    I'll call the tech back up tomorrow to see if it tests those specific switches (I did mention a temp control switch going back from my memory from this forum and he mentioned he tested it, but I'll get more specifics)

    Thanks a lot

  7. #6
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    So your fuse, blower switch, a/c switch, fan clutch, and 384 are good. There are two other connections to 384: one to the ECM and one to a connection in the instrument panel wiring harness labeled "engine overheat warning light". I believe the one to the ECM is an output of the relay. My guess is that the engine overheat connection may be an input to the relay that trips the a/c if such a condition exists. The pressure switch is located below the right (passenger) headlight assembly. To get to it the headlight assembly must be removed. The temp switch is behind the heating/ac housing under the passenger side dash. You have to remove the glove box to get to it. You can check the continuity of the switches with a multimeter. On the pressure switch, pins 1 and 2 should read zero ohms (closed contact) and pins 3 and 4 should read infinite (open contact). The temp switch should also be closed and only open when ambient is 41.5 F or less.

  8. #7
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    Before I check those

    Thanks again for the reply. Before I check those - just wanted to check if this revealed anything interesting:

    1. My overhead lights (the dome lights on the roof of the car between driver/passenger) started to not turn on occasionally (would sometimes take 5 minutes to turn on, or would turn off mysteroiusly). Now however, it appears to not light any more. The only thing I've done differently is tried the wires to the CCM.

    I imagine the CCM has nothing to do with the ECM you mentioned? (the one the AC uses)? Should I think they are related at all? Just wanted to check before digging for these switches.

    Thanks again

  9. #8
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    All the overhead lights get their positive from a plus connection in the wiring harness in the floor from a red / black wire from the CCM. Good chance that connection in the harness is bad. There have been other's that have opened the harness up and cleaned / re-spliced connections in the harness and fixed their problem. Sounds like when you messed with the wires to the CCM, the connection opened up. I don't believe this or any of the wiring to the CCM is related to your a/c problem.

  10. #9
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    More info

    Ken,

    Sure enough, the Red/Black wire to the CCM broke apart when I touched it. This was near the door where 6 red/black wires came together to 1 red/black wire that went to the CCM. I joined them all together again. Overhead lights now work great. There was tons of corrosion on that joint. I also re-did 2 other joints while I was at it (that had corrosion) to make sure they still stayed strong. Admitantly, I didn't really look over all of the cabling because I can't get the carpeting enough to have an easy look, so I basically stuck by the wires by the door.

    You were right on, the A/C still doesn't work. I asked the tech, and he said he tested both of the switches you mentioned above (though I'm not 100% convinced by how he said it). He said he 'overrode' those switches and the A/C didn't kick on.


    You mentioned the ECM (isn't that in the same location of the CCM but on the passenger side?). If so, do you think I should check those wires (or specific colors on that one) to see if the same corrosion happened? I know that when I had flooding, it was on both sides of the car unfortunately.

    Thanks again

  11. #10
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    Great that you fixed the CCM wiring. First, the ECM is located in the front left of the engine in the cowl so I doubt if you would have a corrosion problem like the CCM. If you have a tiptronic transmission, the TCM is located under the carpeting on the passenger side. I question whether the tech really checked the two switches. He should have checked them for continuity with a ohm meter. One test you can do is to pull relay 384 out. The relay should have the terminals numbered or coded. The connector socket for Pin 9 or the "75" labeled terminal of relay 384 should have 12 volts on it when you start the car and turn on the a/c. So measure the corresponding socket for pin 9 for 12 volts. If it does then both switches are okay. The other socket connectors for relay 384 are:
    pin 2 or "30" should be 12 volts fed from fuse 25 with car running
    pin 3 or "31" is ground (check this ground with ohmeter to known good ground)
    pin 8 or "87" goes to the a/c fan clutch. If you jumper 12 volts to the socket for pin 8 the a/c clutch should energize.
    pin 1 or "87a" goes to the ECM. Don't know what if any voltage should be on this connector.
    pin 4 (no label shown) goes to a connection labeled "engine overheat warning light". Don't know what should be on this either with car running.

  12. #11
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    kbhit, I'm in exactly the same situation as you. My a/c clutch doesn't engage even though the secondary fan switches on when the climatronic is taken out of econ.
    I've taken it to an a/c specialist and he can't find anything wrong with it and recommended I take it to a car electrician.

    Was that a VW dealer technician you took the car to?

    Cheers
    Dave

    2000 Passat TDi 115bhp

  13. #12
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    The technician I took my car to wasn't a VW dealer.

    Kenblasko, I've been busy this past weekend so didn't get to testing those out. The past two days I did the cabin filter and air filter so I hope to get to testing the AC either today or by the weekend.

    Though, I did have my car up on a lift this weekend, when we took the splash guard off the button, I did notice a connector near the AC unit (looking at it from the bottom) that wasn't plugged in. Do you know if there's normally a connector that's left unconnected? If that sounds unusual to you I'll try and take a picture of it (though I'll be doing it from the top this time if I can find it). I can't imagine this being the problem but thought it looked fishy - I would imagine any tech would have seen that if that was it.

  14. #13
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    If you are talking about the compressor, there should be an electical connection to the a/c clutch. Otherwise, I don't know what it might be. Maybe someone with a 1.8t can look at their car.

  15. #14
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    have you checked the gas pressure?

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